Holocene hydroclimate changes in continental Croatia recorded in speleothem δ 13 C and δ 18 O from Nova Grgosova Cave

• Published in: The Holocene
• Main Authors: Surić, Maša, Columbu, Andrea, Lončarić, Robert, Bajo, Petra, Bočić, Neven, Lončar, Nina, Drysdale, Russell N, Hellstrom, John C
• Format: Article in Journal/Newspaper
• Language: English
• Published: SAGE Publications 2021
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: http://dx.doi.org/10.1177/09596836211019120; http://journals.sagepub.com/doi/pdf/10.1177/09596836211019120; http://journals.sagepub.com/doi/full-xml/10.1177/09596836211019120

We present the first stable isotope (δ 13 C and δ 18 O) speleothem record from continental Croatia retrieved from two coeval stalagmites from Nova Grgosova Cave. U-Th dates constrain the stalagmite growth history from 10 ka to the present, revealing coeval growth between 7.8 and 5.6 ka. We interpret δ 18 O as an autumn/winter hydrological proxy related to changes of vapor source, precipitation amount, and/or seasonal rainfall distribution, while δ 13 C predominantly responds to spring/summer vegetation status and soil microbial activity. We identify several centennial to millennial-scale hydroclimate oscillations during this period that result from multiple forcing factors. Along with amount and source effect, it appears that some centennial variations were governed also by seasonal moisture balance. From 9.2 to 8.8 ka BP, the local environmental setting was characterized by enhanced vegetation activity, while during the 8.2 ka event the main feature was a change in precipitation seasonality. The most prominent change, identified in both δ 13 C records, is a sudden decline of vegetation and soil biological activity around 7.4 ka, indicating a precipitation decrease at a time of maximum plant growth in spring and summer and likely also reduced precipitation in autumn and winter. Although small in magnitude in these speleothems, a peak in δ 18 O and δ 13 C values at 4.3–4.1 ka suggests that both summer and winter conditions were substantially drier during the 4.2 ka event, in accordance with increased Mediterranean aridity and consistent with other global climate changes reported at this time. Compared to the present North Atlantic Oscillation (NAO) influence, we assume that millennial Holocene NAO-like variations were persistent through the Holocene via their effect on modifying local/regional air temperature, vapor origin, and inter- and intrannual precipitation distribution. Anthropogenic deforestation, which was the first major human impact on the environment during the Neolithic agricultural revolution, is ...